Table Of ContentGuide to Quaking Aspen Ecology
and Management
with Emphasis on Bureau of Land Management
Lands in the Western United States
Paul C. Rogers, Western Aspen Alliance, Wildland Resources
Department, and Ecology Center, Utah State University, Logan, Utah
Guide to Quaking Aspen
Ecology and Management
with Emphasis on Bureau of Land Management Lands
in the Western United States
2017
BLM-UT-G1017-001-8000. 98 p.
Paul C. Rogers
Western Aspen Alliance,
Wildland Resources Department,
and Ecology Center,
Utah State University
Produced in cooperation with U.S.Department of the Interior
Bureau of Land Management
Cooperative Agreement Number: L10AC20552
Guide to Quaking Aspen Ecology and Management
Contents
Chapter 1 – Introduction ...............................................................................................................................................1
How We Got Here ......................................................................................................................................................1
Why Is Aspen Important? ........................................................................................................................................3
Chapter 2 - Aspen: An Evolving Picture .....................................................................................................................7
Issues Affecting Aspen Ecosystems........................................................................................................................7
Science-Management Synergy ..............................................................................................................................12
Chapter 3 - Landscape Interactions And Other Considerations .........................................................................19
Disturbances .............................................................................................................................................................19
Past Management ....................................................................................................................................................21
Ungulate Herbivory.................................................................................................................................................22
Chapter 4 - Aspen Types By Ecological Function ...................................................................................................27
Overview of Functional Types ..............................................................................................................................27
Seral and Stable Functional Types ........................................................................................................................29
Seral Aspen ...............................................................................................................................................................32
Boreal .................................................................................................................................................................32
Montane ............................................................................................................................................................36
Stable Aspen..............................................................................................................................................................40
Parklands ..........................................................................................................................................................40
Colorado Plateau Highlands And Mesas ....................................................................................................43
Elevation/Aspect Limited ..............................................................................................................................47
Riparian ............................................................................................................................................................54
Chapter 5 - Developing An Action Plan ...................................................................................................................57
Setting Objectives ....................................................................................................................................................57
Monitoring: Assess Before Action ........................................................................................................................58
Chapter 6 - Aspen ‘Monitor And Manage’ Toolbox ...............................................................................................65
Selecting from Restoration Actions .....................................................................................................................65
Adapting Management to Monitoring Results ..................................................................................................75
Where to Find More Aspen Information ............................................................................................................77
References .......................................................................................................................................................................81
Appendix 1: Key Terms ...............................................................................................................................................86
Appendix 2: Aspen Stand Condition Rating System .............................................................................................91
Appendix 4: Sample Monitoring Form ....................................................................................................................96
Guide to Quaking Aspen Ecology and Management
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Chapter 1 – Introduction
How We Got Here
Quaking aspen (Populus tremuloides Michx.) have a rich history of
both research and management. Particularly in the American West,
aspen trees stand out as vibrant icons in forest communities dominated
by evergreen-shaded mountainsides (Fig. 1.1). This individuality in
the species piqued the interest of early forest scientists working in the
region, and the fervor has not abated. Early on, though aspen were not
as highly valued as they are today, foresters marveled at the expanses
of this species on desert plateaus and its ability to grow profusely
following fire. Foresters of the early 20th century, however, felt that the C
h
aspen species inhibited development of more valued timber species. a
p
In much of the West, this was also a time of new aspen growth and t
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expansion in response to settlement-era cutting, grazing, and burning 1
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n
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d
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t
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o
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Figure 1.1 Aspen leaf.
Guide to Quaking Aspen Ecology and Management
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(Rogers et al. 2007a; 2011). Later, aspen’s value to humans increased,
particularly as rich understory livestock forage. Managers and
researchers alike became interested in methods of promoting aspen
growth and sustainability. Currently, professionals and the public
are attracted to the benefits of aspen for biodiversity, fire resistance,
recreation, aesthetics, wood products, forage, water conservation, and
wildlife habitat.
Realization of aspen’s usefulness has paralleled a number of threats to
these forest communities. Indeed, some threats may be attributable
to past management actions, such as fire suppression, overgrazing,
water diversion, wildlife management, and inappropriate timber
harvesting methods. In Utah, for example, an estimated 60% of aspen
cover was lost during the 20th century due to past practices (Bartos
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o and Campbell 1998). However, such projections warrant caution, as
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ct they assume that each location with significant signs of live or dead
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d aspen today was once an “aspen forest” where this species comprised
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r the dominant cover. Nonetheless, the 20th century did witness both
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n increases (Kulakowski et al. 2004) and decreases in aspen cover (Di
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– Orio et al. 2005), some attributed to humans and some to the relatively
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r moist climate (Rogers et al. 2011). More recently, reports of “sudden
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pt aspen decline” indicate rapid die-off of both overstory and root systems
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h in some parts of the West (Worrall et al. 2008). Subsequent work has
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linked regional mortality in aspen and recent climate trends (Worrall
et al. 2013). These and other works suggest future climates will acutely
affect aspen on southern aspects and at low elevations, conditions
commonly found on BLM lands across the West. Land managers, then,
face the dilemma of applying the collective knowledge of a large body
of aspen science to specific areas of interest, areas that they cannot treat
as uniform representations of a single species behaving predictably
across its wide range.
In this field guide, I use a “systems approach” to aspen ecology and
management. We have learned much, though perhaps not adequately
communicated, about varying aspen types around our region (Rogers
et al. 2014). For example, what new information is available about fire
behavior in aspen, and how might we best apply that knowledge best
Guide to Quaking Aspen Ecology and Management
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be applied to forest management practices? Or why do aspen forests
vary in their contribution to wildlife management and landscape
biodiversity? Are we as land managers making informed decisions
about stewardship with processes in mind or working against
ecosystem function, which controls such processes? Our driving
paradigm in contemporary land management is to first understand,
then emulate (to the degree possible), ecosystem function. In terms of
western aspen, this means using the best available science and pairing
it with local experience. Where there are knowledge gaps, often field
monitoring and experimentation are required to move forward. These
ideas are not necessarily new, though their application in widely
varying quaking aspen communities provides novel opportunities for
effective management. One key tactic is agency investment in “learning
by doing,” which will be required to adapt to the dynamic institutional
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and ecological conditions expected. h
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Why Is Aspen Important? e
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1
Biodiversity—Among western forests, quaking aspen communities are –
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often the most biodiverse (Kuhn et al. 2011; Chong et al. 2001). Due to n
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the presence of relatively moist conditions and abundant flora, a wide o
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range of wildlife species—both transitory and resident—is drawn to u
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aspen forests (Manley et al. 2000). Thus, it is important to understand t
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that we seek to sustain the range of aspen systems, not just the tree. n
As wildlife habitat, aspen types are often among the most critical
concerns for state and federal agencies charged with managing viable
populations in diverse landscapes
(Fig. 1.2).
Water Conservation—Relatively
high understory biomass,
deep snowpack, and rich soils
allow aspen systems to retain
higherlevels of water in the spring
and early summer (Gifford et al.
1983; LaMalfa and Ryle [sic] 2008).
While further work is needed on Figure 1.2 Biodiversity in aspen.
Guide to Quaking Aspen Ecology and Management
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this topic, these preliminary investigations suggest that retention of
aspen dominance in seral conditions allows deeper infiltration rates,
thereby prolonging water availability later into the season. We expect
similar water benefits in stable aspen systems where conversion to sage
or other dry nonforest types is a possibility. More water in streams
benefits fish as well as downstream human uses.
Aesthetics—People often underestimate the benefit of landscape
beauty to our well-being. Aspen landscapes are iconic in western
North America, especially as their brightly colored autumn leaves
appear. Regardless of activity, white trunks crowned with fluttering
green or gold leaves often lie at the center of our outdoor experience.
In addition to potential spiritual, healing, or calming values found
among the quaking aspen, nature lovers gravitate to this tree for its
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o photogenic qualities.
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t
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u Recreation—Skiing, hunting, biking, hiking, motor touring, camping,
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o fishing, photography, and sightseeing are commonly centered on aspen
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nt scenes. Many western resorts that focus on recreational activities use
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– aspen backdrops in their advertising. Large aspen die-offs, though
1 perhaps endemic to forest ecosystems, are generally unappealing to
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te recreational visitors.
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h Forage—Historically, livestock growers have depended on the diversity,
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biomass, and nutrition of understory aspen communities to feed their
animals. Often found at high elevations, aspen forests provide cooler
and moister conditions for livestock during parched summer months.
Use of forage in these locations, provides direct economic benefit to
western ranchers, as well as indirect benefits to the municipalities
where they reside.
Fire Protection—Forests dominated by aspen are less prone to high-
intensity burning compared to surrounding conifer types (Shinneman
et al. 2013). In wildland urban interface (WUI) situations, aspen may
be used as a firebreak around developed areas (Fechner and Barrows
1976). Thus, management that favors aspen (i.e., thinning conifers,
light underburning) may be used as a prudent means of protecting
homesites.
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